1. Field of the Invention
This invention relates to a gyroscope and an input apparatus having the gyroscope, more particularly relates to a gyroscope that detects the displacement of a leg of a tuning fork caused particularly when the angular velocity is supplied in the form of change in capacitance and an input apparatus having the gyroscope.
2. Description of the Related Art
Heretofore, the gyroscope having a tuning fork formed of conductive material such as silicon has been known. The gyroscope of this type detects the vibration in the direction perpendicular to the vibration direction caused by Coriolis force when a leg of a tuning fork is vibrated in one direction and the angular velocity with the center axis in the longitudinal direction of the leg is supplied during vibration. Because the magnitude of the vibration caused by the Coriolis force corresponds to the magnitude of the angular velocity, the gyroscope can be used as an angular velocity sensor, it can be applied to, for example, the coordinate input apparatus of a personal computer.
FIG. 19 is a diagram for illustrating the structure of a tuning fork that is the main component of the conventional gyroscope. As shown in FIG. 19, the tuning fork 100 of this example has three legs 101 and a support 102 which connects the three legs to base ends of each leg 101 and is formed of silicon that has been rendered conductive. The tuning fork 100 is fixed to a substrate 103 with the support 102, and driving electrodes (not shown in the drawing) are provided under the corresponding legs 101 respectively. As the result, the electrostatic attractive force caused when a voltage is applied to a driving electrode causes vibration of each leg 101 in the vertical direction.
In this gyroscope, the angular velocity having the rotation axis in the longitudinal direction of the leg 101 supplied to the leg during vibration in the vertical direction causes the vibration in the horizontal direction, the vibration in the horizontal direction is detected by means of a pair of detecting electrodes 104 disposed on both sides of each leg 101. In detail, when the gap between the detecting electrode disposed on one side of a leg 101 and the leg 101 is narrowed and a gap between a detecting electrode 104 disposed on the other side of the leg 101 and the leg 101 is widened concomitantly with horizontal displacement of the leg 101, two pairs of electrostatic capacitance formed by the detecting electrodes 104 and legs 101 are changed. The magnitude of input angular velocity is detectable based on the electrostatic capacitance change.
In the case of the gyroscope having the structure described herein above, the gap between a leg 101 and an adjacent leg 101 (referred to as inter-leg gap hereinafter) cannot be narrowed unlimitedly because detecting electrodes are provided on both sides of each leg 101. The inter-leg gap is G=2x1+3x2 wherein the width of a detecting electrode 104 is denoted by x1 and the gap between a detecting electrode 104 and a leg 101 and the gap between detecting electrodes adjacent each other are denoted by x2. Because of work limit of x1 and x2 in silicon work to which general semiconductor device fabrication technique is applied, the narrow inter-leg gap G has been limited.
On the other hand, it has been found that the reduction of the inter-leg gap G of a three-leg tuning fork leads to the increased xe2x80x9cQ valuexe2x80x9d that is the performance index for representing the magnitude of resonance of a device of this type. The increased Q value contributes not only to improvement of detection sensitivity of angular velocity but also to improvement of conversion efficiency from the electric energy supplied to a device to the vibration energy, and as the result the driving voltage can be reduced.
However, though it is estimated that the reduced inter-leg gap is advantageous in miniaturization of a device, improvement of detection sensitivity, and reduction of driving voltage, because of the limitation on the reduction of the inter-leg gap of the conventional gyroscope, the increased Q value has not been realized.
The present invention has been accomplished to solve the above-mentioned problem, and it is the object of the present invention to provide a high-quality and low-cost gyroscope that is variously advantageous as described herein above and an input apparatus that uses the gyroscope.
To achieve the above-mentioned object, a gyroscope of the present invention is characterized by comprising a tuning fork formed of conductive material having vibrators and a support for connecting the base ends of the vibrators, driving electrodes for driving the vibrators in capacitance coupling with the vibrators, and at least one detecting electrode for each vibrator disposed correspondingly to the vibrator so as to face at least partially to the end face of the vibrator in the extending direction for detecting the capacitance formed between the detecting electrode and the end face.
The gyroscope of the present invention operates based on the detection principle that the vibration of a vibrator (corresponding to the above-mentioned xe2x80x9clegxe2x80x9d) of a tuning fork is detected in the form of capacitance change like the conventional gyroscope. Usually, the capacitance C is represented as shown in the following.
C=xcex5xc2x7(S/d)xe2x80x83xe2x80x83(1)
wherein xcex5 denotes a dielectric constant, S denotes the surface of an electrode, and d denotes the gap between electrodes.
In the case of a conventional gyroscope, the change of the gap between a leg and a detecting electrode concomitant with vibration, namely capacitance change due to the change of the gap between electrodes d in the above-mentioned equation (1), is detected. On the other hand, in the case of a gyroscope of the present invention, the change of the facing area of a leg to a detecting electrode concomitant with vibration, namely capacitance change due to the change of the electrode area S in the above-mentioned equation (1) is detected. The detection in the conventional gyroscope is different from the detection in the gyroscope of the present invention in that point.
In other words, the gyroscope of the present invention is structurally featured in that a detecting electrode at least partially facing to the end face of a vibrator in the extending direction to form a capacitance between the detecting electrode and the end face of the vibrator is provided. Because of the structure, the vibrators of the tuning fork are vibrated when a voltage is applied to the driving electrode, and when the angular velocity having the rotation axis in the longitudinal direction of the vibrator is supplied in that state, vibration in the direction perpendicular to the above-mentioned vibration direction is caused. At that time, because the end face of the vibrator is facing to the detecting electrode, and the facing area of the end face to the detecting electrode changes concomitantly with vibration of the vibrator, the capacitance change is caused. The angular velocity can be detected by detecting the capacitance change.
Therefore, in the case of the gyroscope of the present invention, the detecting electrode may be provided on the extension line in the longitudinal direction of the vibrator, and it is not necessary to provide the detecting electrode between a leg and an adjacent leg unlike the conventional gyroscope. As the result, the inter-leg gap can be minimized to the work limit of the material of the tuning fork, for example, work limit of silicon, and Q value is thereby increased, the detection sensitivity is improved, and the driving voltage is reduced. Of course, the device is miniaturized.
At least one detecting electrode may be provided for each vibrator. In other words, in the case that one detecting electrode is provided, the capacitance change of one capacitor involving one detecting electrode and one vibrator may be detected. In the case that two detecting electrodes are provided, for example in the structure that the vibrator is driven in the vertical direction, two detecting electrodes may be arranged horizontally so as to face to one end face of one vibrator. In this case, two capacitors are formed from two detecting electrodes and one vibrator, and when the vibrator is vibrated in the horizontal direction, the capacitance of one capacitor increases some magnitude then concomitantly the capacitance of the other capacitor decreases the same magnitude. Therefore, by detecting the difference between two capacitance changes, doubled capacitance change is obtained from the same vibration, and the detection sensitivity is improved preferably.
The driving electrode may be formed extendedly in the extending direction of each vibrator, and may be disposed at least on one side face of the tuning fork and at the position corresponding to each vibrator. In this case, each vibrator is vibrated in the vertical direction with respect to the tuning fork and the vibration due to resonance is horizontal. The gyroscope of the present invention is by no means limited to the case in which the vibrator is driven in the vertical direction and the horizontal vibration is detected, and the gyroscope of the present invention can be applied to the case in which the vibrator is driven in the horizontal direction and the vertical vibration is detected.
The input apparatus of the present invention is characterized in that the above-mentioned gyroscope of the present invention is used. By using the gyroscope of the present invention, the small-sized apparatus such as a coordinate input apparatus of a personal computer is realized.
Another gyroscope of the present invention is characterized by comprising a tuning fork having vibrators formed of conductive material and a support for connecting the base end sides of the vibrators, driving electrodes for driving the vibrators in capacitance coupling with the vibrators each other, and detecting electrodes provided at least above or under one side face of the tuning fork so as to face to the ends of the vibrators for detecting the capacitance formed between at least one detecting electrode and the vibrator that are facing each other.
The above-mentioned another gyroscope of the present invention operates based on the detection principle that the change of the facing area of a leg to a detecting electrode concomitant with vibration, namely capacitance change due to the change of the electrode area S in the above-mentioned equation (1) is detected. In the case of a conventional gyroscope, the change of the gap between a leg and a detecting electrode concomitant with vibration is detected. The detection in the conventional gyroscope is different from the detection in the above-mentioned another gyroscope of the present invention in that point.
In other words, the above-mentioned another gyroscope of the present invention is structurally featured in that at least one detection electrode for detecting the capacitance formed between this detection electrode and the vibrator is disposed at least above or under one side face of the tuning fork so as to face to the end of the vibrator. Because of the structure, the vibrators of the tuning fork are vibrated when a voltage is applied to the driving electrode, and when the angular velocity having the rotation axis in the longitudinal direction of the vibrator is supplied in that state, vibration in the direction perpendicular to the above-mentioned vibration direction is caused. At that time, because the end face of the vibrator is facing to the detecting electrode, and the facing area of the end face to the detecting electrode changes concomitantly with vibration of the vibrator, the capacitance change is caused. The angular velocity can be detected by detecting the capacitance change.
Therefore, in the case of the above-mentioned another gyroscope of the present invention, the detecting electrode may be provided above or under one side face of the vibrator, for example on the substrate in the case that the vibrator is supported on an arbitrary substrate, so as to face to the vibrator, and it is not necessary to provide the detecting electrode between a leg and an adjacent leg unlike the conventional gyroscope. As the result, the inter-leg gap can be minimized to the work limit of the material of the tuning fork, for example, work limit of silicon, and Q value is thereby increased, the detection sensitivity is improved, and the driving voltage is reduced. Of course, the device is miniaturized.
It is desirable that the driving electrode is formed extendedly in the extending direction of each vibrator and disposed at least above or under one side face of the tuning fork at the position that faces to each vibrator, and the detecting electrodes are disposed apart from the driving electrode to prevent the parasitic capacitance between the driving electrode and the detecting electrode. If the parasitic capacitance is generated between the driving electrode and the detecting electrode, when the angular velocity is detected to detect the capacitance change generated between the vibrator and the detecting electrode, the parasitic capacitance is also detected undesirably to cause noise component, and SN ratio is decreased disadvantageously. If the driving electrode and the detecting electrode are disposed separately each other with a sufficient space, such disadvantage is prevented.
At least one detecting electrode may be provided for each vibrator, otherwise a pair of electrodes that faces to each vibrator may be used as each detecting electrode and the pair of electrodes may detect two capacitances formed between the respective electrodes of the pair and the end of each vibrator. In detail, in the case that one detecting electrode is used, the capacitance change of one capacitor formed by one detecting electrode and one vibrator may be detected. In the case that the detecting electrode is disposed correspondingly to the end of each vibrator, because the displacement of each vibrator is the maximum at the end, the maximum capacitance change is detected. On the other hand, in the case that one pair of two detecting electrodes are provided, two capacitances are formed by two detecting electrode and one vibrator, and when the vibrator is vibrated in one direction, the capacitance of one capacitor increases and the capacitance of the other capacitor decreases by the same magnitude concomitantly. Therefore, in the case of this structure, detection of the difference between two capacitance changes brings about doubled capacitance change for the same vibration, and the detection sensitivity is improved preferably. The total capacitance value is preferably 0.1 pF or larger.
Another input apparatus of the present invention is characterized in that the above-mentioned another gyroscope of the present invention is used. By using the above-mentioned another gyroscope of the present invention, the small-sized apparatus such as a coordinate input apparatus of a personal computer is realized.